Method for annealing sheet metal



Aug. 5 1924. 1,503,639

o. H. CUNNINGHAM METHOD FOR ANNEALING SHEET METAL Filed Sept. 25 1922strength.

Patented ug. 5, 1924.

OTTO H. CUNNINGHAM, 0F LEECHBURG, PENNSYLVANIA.

METHOD FOR ANNEALING SHEET METAL.

Application filed September 25, 1922. Serial No. 590,298.

To all whom it may con/cem.' Be it known that I, O'rro H. CUNNING- HAM'.a citizen of the United States, and a resident of'Leechburg, in thecounty of Armstrong and State of Pennsylvania, have made a new anduseful Invention in a Method for Annealing Sheet Metal, of which the`following i-s a specification.

kThe invention has for its objects the provision of a method which willanneal sheet metal more rapidly and economically than the methods andapparatus heretofore eniployed and which will give ,a better product.

Under the present practice the annealing box, with its pack of plates orsheets, is placed in a furnace and gradually raised through a period ofseveral hours to a temperature of approximately 1500o F., after whichthe temperature of the furnace is maintained for two or more hours, this.part of the operation being known as soaking, and being regarded asessential to proper anneallng. The furnace is then allowed to cool verygradually during a period `0f several hours until a temperature of about900 F. in the pack is reached and the plates are dark red in colorV`V orblack. At this time, the box is withdrawn from the furnace and opened. l

This procedure is long-drawn out and involves a high fuel cost. onereason being the requirement of securing a uniform heating throughoutthe pack, since the box and pack are heated progressively from theoutside inward. This means that in order to secure. a proper heat at thecenter of the pack, the outer portions must be heated to a much greaterdegree than would otherwise be necessary, which not only involves awaste of heat, but also involves a detrimental degree of over-heat inthe outer parts of the pack tending to produce defects in the sheets andreduce y their tensile My apparatus and proc'ess are designed toovercome the foregoing objections and to give a more rapid and uniformheating of the pack and a reduced cost. Briefly stated, this isaccomplished by the use of electrical heating element 'suitablydistributed throughout the pack `so that the tedious process of heatingfrom the outside inward progressively is avoided. The outside heat fromya furnace may still be ap plied if' desired, but only a fraction oftheoutside heat heretofore necessary need be applied, and thedesired degreeof heat throughoutl the pack may be secured ina much shorter periodof-time. Apparatus embodying the invention is illustrated in theaccompanying drawings wherein:

)Figure 1 is a vertical section through the apparatus in use; Fig. 2 isa plan view of one form of heating element; and Figs. 3 and 4 are detailviews of another form of heating element, Fig. S/being a partialplanvieiw, and Fig. 4 a section on the line IV-IV of Fig. 3; and Fig. 5 is asection on an enlarglgd scale through the vresistance element` of gs. 3and i4.

Referring to Fig. 1, the numeral 1 indicates the annealing boXf restingupo f the base plate 2 with its lower edge embe ded in the sand in the'groove 3 in order to exclude the air which would oxidize the metalduring the annealing process. 4 is a pack of sheets which are to besubjected to the annealing operation, and 5l indicates the walls ofthefurnace in which the box 'is placed in case furnace heat is employedtosupplement the heating effect of the interior electrical heating means.The interior heating means comprises the plurality of plates- 6interspersed between the sheets of the pack as indicated and providedwith suitable electrical heating means. will be understood that thenumber may be increased or decreased depending upon conditions. Thecharacter of the plates and the resistanceJ elements carried therebylmay be widely varied and the invention is limited to Kno particularconstruction of heating element. As shown in Figs. 1 and 2 the plates 6are of insulating material, suchas magnesia, clay or porcelain, suitablyrem-4 forced if necessary and perforated transversely as indicated at 7to receive the heating wire 8. This wire is woven back and forthythrough the plates as indlcated 1n Fig.' 2 and consists of suitablereslstance metal such as nichrome. The various heating wires areconnected in parallel by means of the wires 9 and 10 as indicated whichare inturnfconnected to the leads 11 and 12 extending through the Wallsof the an-` box and suitably sealed and insulated nealin at sucl points.U

Figs. 3 and 4 illustrate a modified form of heating element which may beemployed. In this construction a metal plate 13 1s used Four plates 6are illustrated, but it provided with the grooves 14; and 15 on theupper and lower sides thereof. The resistance element in this device iswhat is known as sheathed wire, consisting of a` member 16 made up of aresistance Wire of nichrome or similar metal surrounded by an insulatingsheath of clay or composition enclosed in a metal tube.

The member 16 is Woven back and forth in the grooves 14 and 15 asindicated in the drawingsand as used With a metal plate gives a verydurable and effective resistance element for the particular heatingservice here required, as it may be handled and subjected to the weightof the pack of sheets Without breakage or injury.

. In carrying out the process, the heating elements are placed in thepack as indicated in Fig. 1, and current applied to heat the pack, andbring the temperature up to a point in the neighborhood of 1500o F. Thismay be accomplished either by the use of .the electrical heating meansalone, or the annealing box may be placed in an annealing furnace, asindicated in Fig. 1, and the heating accomplished by the jointapplication of heat from the furnace and that from the electricalheating elements. In this Way the pack is brought to a relatively hightemperature and at a more uniform rate throughout the pack than is thecase Where the pack is heated from the outside alone as has heretoforebeen the practice. After the temperature of the pack has been raised tothe desired point, such temperature is maintained to give a soakingaction, after Which the temperature is allowed to fall slowly until atemperature of 800 or 900 F. is reached when the box is opened and thepack removed.

The apparatus is capable of considerable modification Without' departingfrom the in` vention involved. Only one form of annealing box isillustrated with the plates of the pack in horizontal position and withall of such plates in a single casing, but it will heating units, inwhich case the box would oe constructed of heat insulating material andif desired, other forms of electrical heating units than theinterspersed units illustrated might beV employed, the processcontemplating broadly the annealing of th(l sheets by electrical heatingmeans applied internally of the box or casing. What I claim is 1. Aprocess of annealing a pack of iron sheets which consists in heating thesheets in an enclosed space by applying electrical heating means in saidspace between the sheetsof the pack.

2. A process of annealing a pack of iron sheets which consists inenclosing the sheets in an annealing box, applying heat to the exteriorof the box, and applying additional heat to the interior of the box at aplurality of different levels betweenthe sheets of the pack to carry thetemperature of the pack through its annealing range.

In testimony whereof, I have hereunto subscribed my name this 22nd dayof Septomber, 1922.

OTTO H. CUNNINGHAM.

